How-to/Can-we use serverless for modifying existing cloudformation stack?

Let's say, I have deployed my lambda and API gateway using cloud formation. Now I want to start using the serverless framework, so how do I point my new serverless template to point to existing cloud formation stack to make changes? Is it possible? If yes then how? Can someone please give a small example or reference docs? I know I can drop the existing resources and recreate them but that is not a good option for me.

If this happens successfully then I am going to use to this in my production so let me know of any worst-case failure scenarios also. Will my template delete everything and recreate or it will just override on my existing stack?

Thanks for helping : )

No files, tests, or entry points are named. First determine whether Serverless Framework can adopt an existing CloudFormation stack, then document a minimal example and the expected update, deletion, recreation, and failure behavior; done when the migration guidance answers those production concerns.